IN TOUCH WITH NATURE

Otago Daily Times, Issue 20320, 31 January 1928, Page 2

IN TOUCH WITH NATURE

THE LADYBIRDS. By J. Dkumjiond, F.L.S., F.Z.S. It is somewhat strange that up to the present lime little lias been known of uie life history of one of the most beneficent insects introduced into New Zealand and known in the Old Country Images. This is the eleven-spot ladybird, wnose bright red wing-cases are embellished with black spots. Ladybirds—there are moie than 2uoo species of them —are members of tho great family of the beetles, in that family the eleven-spot ladybird has occupied an anomalous and incomprehensible position. Jiright sunshine, fresh air, and the company of plants, it was believed, were the pleasant conditions in which its spent its life from its emergence from the egg to its stage a periect ladybird. Messrs O. A. Mer-ntt-Hawkes and T. F. Marriner, two English entomologists, in their efforts to discover the eleven-spot ladybird’s life history, shatter that belief. They find that tho insect spends part of its life in the warmth, moisture and darkness of a pad of dung, eating semi-decayed food prepared tor it by moulds and dactoria. It does not spend all its life in that repugnant environment, but, in its later stages, hunts and destroys aphids, miteij and scale insects.

Messrs Merrritt-Hawkcs and Marriner, who have published the results of their inquiries in Discovery, a London journal edited by Mr J. A. Beni), state that a female eleven-spot ladybird, before laying, seeks a dung pad, which must be neither too damp nor too dry, neither too warm nor too cold, and must have a hole in its surface leading into passages that will admit her with ease. She is guided by her olfactory organs. Walking down a passage, she chooses a position for her eggs. The dung pad throbs with life. Day and night many small insects pass up and down the, passages. To protect her eggs from those enemies the ladybird usually hangs the eggs from the roof of a passage.

They hang there, each embedded at its base in the dung, in batches of from 5 lo 23. In four or five days the shells break and colourless grubs push out their heads and their front legs. Emergence is not complete until five or six hours have elapsed. The newly-born grubs then are almost black. Almost immediately they set to work on the abundant food above them, under them, and all around them. Two days see the end of the first stage of development. After a brief rest while the skin is cast, feeding is resumed. At the end of four more days there is another change of skin. The grub then is much larger. It is so sensitive that if it is disturbed by even a shadow it curls up its somewhat long legs and pretends to be dead. This sensitiveness is less marked at the end of the third stage.

When the fourth and last stage is reached the grub has changed not only its size and colour but also its nature, it has grown and it is deep black with a bluish bloom. Leaving the darkness and the mire of the dung-pad for a higher and brighter life it wanders over the surface of its old home and on to grassblades or other plants probably to feel on greenfly and other insects. There it enters its chrysalis stage spent sometimes on tho surface of the dung-pad, sometimes just inside a passage. The chrysalis stage occupies a week. There comes out, the glory of the wonderful n etamorphoscs in those odious conditions, from 20 to 32 days after the egg was laid, a lovely ladybird, with soft, spotless, bright yellow wing cases. Before many hours have passed, the bright spots have ap-, peared, and the bright yellow has changed to brilliant red. In that conspicuous costume the ladybird flics off to eat aud to find mate.

The rounded convex form of ladybird, with its pretty coat, is one of the best known objects in the insect world. It is not generally known that the ladybird is a beetle, although it doc-s not share the popular prejudice against many members of its order. Children shrink from most beetles; they have no hesitation in allowing a ladybird to crawl on their hands. Many beetles —the borers, for instance —are injurious in their grub stages only. In their grub stage ladybirds do their best work.

A perfect female flies in the sunshine inspecting plants attacked by, the aphis and the scale-insects. Selecting one that will be useful to her young, on account of the numbers of those insects on it, she there lays about 20 eggs close together. As soon as they arc hatched they begin their useful work on aphis or scale-insect. Making good use of their six-jointed logs, they are much more active than the grubs of most other insects. In an hour, one ladybird grub destroys from 30 to 40 greenflies. A squad, in a single day, will completely clear a badly infested leaf. Four or five weeks are spent in the grub stage. Fastening its tail to the under side of a leaf or a twig, and banging head downwards, the little grub awaits the impulse that rends its husk. Its skin splits down the back, and is thrust off, and the grub becomes r. short, stout, spotted chrysalis, wide’- gives place to a most perfect ladybird. Its useful ork is not finished. The perfect insect continues to war on injurious insects until it dies. There is a belief that the conspicuous spots on the grub and chrysalis, and the perfect ladybird’s colours, warn insecteating birds that this insect at least is unpalatable.

The ichneumon, a notorious parasite, seems to leave the ladybird -lone; but the eleven-spot is heavily attacked by a fly, which lays its eggs in the body of a ladybird grub. When these hatch out the grub is eaten by the parasite. A dung-feeding beetle, Aphodius, has been convicted of killing eleven-spot ladybirds in the t,i..b and the perfect stages, but not of eating them. A fungus, name unknown. which lives in dung, is fatal to the grub.

Possible enemies may be repulsed by a very unpleasant smell from the ladybird's blood, a yellow fluid that exudes from the joints of the ladybird’s legs when it is touched. When towns in England were invaded by hosts of ladybirds from Europe, streets being red with them, a thick band of the intjaders ran along the angle of the walls and ceiling of a room like a red cable. The unpleasant smell, amplified perhaps 10.000 times, became almost unbearable. Even after the room was cleared, it was hardly habitable, as the windows could not be kept open, on account of the swarms that waited outside to gain admission.

Amongst New Zealand’s own 15 species of ladybirds, there is a very small ml very inconspicuous one that feeds on jumping plant-lice, whose young gather in great numbers on tlie young foliago of gums, wattles, and the native fuchsia tree. One of these, the eucalyptus sapsucker, probably feeds on globules of fluid exuded by the bluegum. It makes ■ comfortable white woolly covering (nr itself. Its small, yellow, oval eggs, pointed at each end. are laid in clusters on the opening leaves of buds. The yellowish minute young, embellished with purple markings, soon grow into robuster black forms with white markings. Then comes the final stage, characterised by four wings and dark, ‘narrow bodies, the abdomen a rich vellow, with many black hands. This insect, when disturbed, leaps off the leaf. If large numbers are present, the shaking of the foliage brings down a shower of them. Some jumping plant lice produce, in minute pearlv glob ides, honeydew, which ants raid. All arc skilful jumpers.

But the ladybird's favourite victim, all the world over, almost, is the aphid, plant lice or #reen fly, one of the worst pests

that trouble man. Parthenogenesis, the production of young from unfertilised eggs, is so marked amongst anhids that tliev increase amazingly. Virgin females -jive birth to living female young when only seven or eight days old. Reproduction by unfertilised eggs is repeated again and again through the summer months, young produced in this way producing young by the same process. As estimate of the number of progeny of a single female aphid, if uninterrupted, in 10 years, is almost too sensational for publication. Ladybirds are not protected by law, but they should be.